Synthetic fiber is used in various materials by weaving a high-density fabric. Among others, an airbag application is important.
An airbag module is a safety device for restraining an occupant in a collision of a vehicle, and consists of a collision sensor, an inflator as a gas generator, and an airbag. The airbag is formed of a synthetic fiber fabric and withstands heat in a reaction of a propellant of the inflator, deploying in several tens of milliseconds, and absorbing the thrusting energy of the occupant with the inflation gas of the deployed bag.
The airbag must have mechanical properties high enough to not rupture during deployment or thrusting of the occupant, and physical properties satisfying the necessary mechanical properties are designed by a high-density fabric. The uniformity of the weave density of a fabric is a factor supporting the uniformity of mechanical properties, and there is a demand to enhance the uniformity of the weave density.
Also, the airbag needs to be deployed in a moment by gas and is preferably non-air-permeable as much as possible, and a coated fabric provided with a coating film of a resin or an elastomer is used, or a non-coated fabric made to be low air-permeable by high-density weaving is used. The uniformity of air permeability of the fabric leads to the uniformity of action properties of the airbag. Furthermore, at the instantaneous deployment by gas, local gas permeation due to an air permeability unevenness results in local concentration of a deployment stress, giving rise to a rupture of the airbag, and therefore, there is a demand to enhance the uniformity of the air permeability.
In the high-speed weaving of a high-density fabric, very severe friction occurs between a warp yarn and a reed or a heddle when feeding a warp yarn to a loom, and the warp yarn may be disentangled and substantially fail in forming a sufficient opening, as a result, a weft yarn is not smoothly inserted, producing a fabric defect or stopping the loom. To avoid such a problem, it is known to prevent disentanglement of the warp yarn by sizing the warp yarn or converging warp yarns with an oil/fat material or by air interlacing.
Patent Document 1 below discloses a technique of improving the weavability by improving the entanglement of the weft yarn. However, there is a problem that the physical properties of the fabric cannot be uniformly maintained at the time of high-speed weaving a high-density fabric. That is, with respect to weft insertion in a high-speed shuttleless loom, the loom can be prevented from stopping by making the weft yarn entering from the nozzle side to arrive at the side opposite the nozzle, but with respect to the weft traveling property, the arrival speed is extremely varied and there arises a problem that the uniformity of the fabric property is impaired.
Recently, in airbag applications, development is being made with an attempt to reduce the weight of a fabric by using a yarn of synthetic fiber having small fineness and high tenacity, but smaller fineness requires higher density and for realizing this, weaving at a higher speed is demanded. Also, it has been difficult to ensure the uniformity of air permeability in a non-coated fabric made to be low air-permeable by high-density weaving. In the airbag application, for directly linking the uniformity of weave density or the uniformity of air permeability to the airbag performance, it is required for a synthetic fiber having smaller fineness and higher tenacity to improve the uniformity of physical properties of a fabric woven in high-speed weaving.